Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é a categoria Masculina 50 que possui um Senior Misto de n/A, e um Masculino Aberto de gold coast sharks def sydney mets, e um Masculino 30 de sydney mets def sydney scorpions, e um Feminino u20 de southern suns def brisbane city cobras?
 ###Tabelas: CREATE TABLE key (key_id AUTO_INCREMENT PRIMARY KEY, Nationality VARCHAR, Position VARCHAR, Tottenham Hotspur career VARCHAR, Club Apps VARCHAR, Goals VARCHAR) CREATE TABLE tv_services_for_sky_italia_costumers (tv_services_for_sky_italia_costumers_id AUTO_INCREMENT PRIMARY KEY, Television service VARCHAR, Country VARCHAR, Language VARCHAR, Content VARCHAR, HDTV VARCHAR, Package/Option VARCHAR) CREATE TABLE foreign_players (foreign_players_id AUTO_INCREMENT PRIMARY KEY, Country VARCHAR, Player name VARCHAR, Period VARCHAR, Position VARCHAR, Matches VARCHAR, Goals VARCHAR) CREATE TABLE mlb_draft_history (mlb_draft_history_id AUTO_INCREMENT PRIMARY KEY, Draft Year INT, Player VARCHAR, Summer Team VARCHAR, College VARCHAR, MLB Team VARCHAR, Draft Round VARCHAR) CREATE TABLE results_by_year (results_by_year_id AUTO_INCREMENT PRIMARY KEY, Year INT, Men's Open VARCHAR, Women's Open VARCHAR, Mixed Open VARCHAR, Men's u20 VARCHAR, Women's u20 VARCHAR, Senior Mixed VARCHAR, Men's 30 VARCHAR, Women's 30 VARCHAR, Men's 35 VARCHAR, Women's 35 VARCHAR, Men's 40 VARCHAR, Women's 40 VARCHAR, Men's 45 VARCHAR, Men's 50 VARCHAR)  
SELECT Men's 50 FROM results_by_year WHERE Senior Mixed = n/a AND Men's Open = gold coast sharks def sydney mets AND Men's 30 = sydney mets def sydney scorpions AND Women's u20 = southern suns def brisbane city cobras